1. Field of the Invention
The present invention relates generally to large scale batch manufacturing facilities, and more specifically to the optimization within such facilities.
2. Related Art
Batch manufacturing is a dominant method of producing a number of valuable products such as food, beverages, specialty chemicals, pharmaceuticals, etc. An overview of the biopharmaceutical production process and its associated plant design, for example, can be found in U.S. Pat. No. 6,311,095, issued Oct. 30, 2001 and U.S. patent application Ser. No. 09/373,793, filed Aug. 13, 1999, both having common inventorship and are hereby incorporated by reference in their entireties.
The scheduling of equipment utilization in these batch processes tends to be complex relative to other industries that use continuous or repetitive manufacturing procedures. This complexity often results in an oversizing and/or underutilization of equipment in batch processes to meet a required production capacity per batch cycle due to a general lack of well-defined rules for batch process scheduling.
In batch manufacturing, repeating cycles of product batches are often scheduled to begin at a fixed repeating interval or batch cycle offset (BCO). For example, a new batch of a pharmaceutical product may begin each Monday morning at 7 AM. In this case, the BCO would be equal to 7 days. Determining the BCO is often an arbitrary practice based on convenience rather than clearly defined process optimization procedures. In addition, batch processes are frequently designed to have a minimal batch cycle duration (BCD) regardless of the duration of the BCO. Often, however a short BCD is required due to the instability of the product. In other cases, the BCD it is kept to a minimum in order to minimize the overlap of concurrent batch cycles and minimize the complexity of scheduling in manufacturing operations. (This overlap factor is a function of the BCD divided by the BCO. For example if a batch process has a BCO=2 days and a BCD=10 days then when the process reaches steady state there will be 10/2=5 batch process at different stages of completion simultaneously at any given moment provided the values for BCO and BCD remain constant.)
Existing batch design practices typically focus on cycling equipment for a given unit operation one or more iterations per batch cycle in order to increase equipment utilization. These practices, however, fail to define an optimal relationship between these cycles and the BCO that both maximizes the number of theoretical batches per year for a given production quantity and maximizes the number of equipment cycles per batch. As a result, these conventional practices do not allow for optimal equipment utilization and lowest cost of goods (COG) for batch manufacturing.